Australian news report

For almost half a century, the United States has dominated the exploration of Mars from the first grainy black-and-white pictures of the craggy surface to the more recent discovery of ice.

Now, budget woes are pushing NASA toward a joint exploration venture with Europe.

By 2016, the US may unite with the European Space Agency for future Mars trips - a move that would mark a significant shift for NASA.

Details of such a union could come by the end of this month.

Talk of a possible marriage has unnerved some space advocates who worry a union will decrease competition and cause the US to lose its edge, holding it hostage to foreign politics.

"NASA should be showing off its stuff and not saying, 'We can't do it unless we have the cooperation,"' said Robert Zubrin, a former Lockheed Martin Corp engineer who now heads the Mars Society advocacy group.

The trans-Atlantic dialogue comes at a critical point. NASA is polishing a new public relations message to replace its decade-old focus on finding water.

At the same time, Mars is facing competition from other solar system bodies emerging as promising places to search for signs of life.

While international pairings are nothing new, they tend to be more common on deep space missions.

NASA united with the European and Italian space agencies to launch the Cassini-Huygens mission to Saturn and its moon Titan.

Earlier this year, NASA and the European agency announced plans to be partners on a 2020 mission to Jupiter's ice-covered moon Europa.

With Mars, however, NASA has kept a do-it-yourself attitude while letting other countries add instruments to NASA spacecraft for their own data-gathering.

That NASA and the Europeans are considering pooling resources reflects a budget reality: It has become too expensive for one nation to pay to go to Mars alone, especially with a long-term goal of returning Martian rocks and soil to Earth estimated to cost at least $US5 billion.